1. Field of the Invention
The present invention relates to an auto focusing apparatus and method preferred for use in the case of automatic focusing for shooting, and to an image sensing apparatus, and more particularly, relates to an auto focusing apparatus and method preferred for use in the case of extracting a feature portion (in particular, a face portion) of a person and exercising focusing control on the basis of the result, and to an image sensing apparatus.
2. Description of the Related Art
In autofocus (AF) control for video cameras, etc., a TV-AF method is a primary method, in which an AF evaluation value signal is generated which represents the sharpness (contrast) of image signals generated using an image sensor, and the position of a focus lens is searched such that the AF evaluation value signal reaches its peak value.
The autofocus control based on the sharpness of video signals may, for example, in the case of photographing a person, fail to focus on the person and focus on the background instead, because of the relationship in contrast between the person as a main subject and its background.
In order to solve this problem, a technique has been developed in which autofocus control is carried out using the result of face recognition in an image sensing apparatus provided with a face recognition function for recognizing a face included in an image with image signals. For example, Japanese Patent Laid-Open No. 2006-227080 discloses a technique in which a focus detection area including a recognized face region is set to carry out focus detection. Furthermore, Japanese Patent Laid-Open No. 2001-215403 discloses a technique of detecting eyes of a person and carrying out focus detection on the basis of the detected eyes.
As it happens, in the case of focus detection using the face recognition function described above, focusing control for recognized faces is constantly carried out. For example, in order to focus on a face recognized by the face recognition function, a focus detection area is set to correspond to the position of the recognized face. In a case in which no face has been recognized, a focus detection area is set in a predetermined fixed position within a shot image such as, for example, in the center position of a shot image. On the basis of an AF evaluation value generated from image signals in the focus detection area, focusing control is carried out.
In a case in which the main subject is a person (hereinafter referred to as a main person), there is a possibility that face recognition will be difficult depending on the influence of change in composition or the influence of camera shake of the photographer, and it is not always true that a face is constantly recognized. In particular, in the case of shooting moving images, the main person is often moving, and the camera will thus fail in face recognition even if the camera has succeeded in face recognition in the last minute, in a case in which the main person looks away or another subject temporarily obscures the main person.
If the state in which a face is recognized and the state in which the camera has failed in face recognition alternate frequently within a short interval when the face actually exits in the same position within a shot image, it will be difficult to determine where to focus. In this case, there is a problem that there is a possibility that focusing control will be unable to be carried out in a stable manner, such as slower focusing operation for a main person desired by the photographer or the inability to carry out focusing.